1. Field of the Invention
An aspect of the invention relates to a system for processing and transmitting a digital broadcasting signal and a method thereof that robustly processes and transmits a digital broadcasting transport stream, and more particularly to a system for processing and transmitting a digital broadcasting signal and a method thereof that robustly processes and transmits a digital broadcasting transport stream using a system having a simple construction that performs a robust data process on a robust stream in a dual transport stream including a normal stream and the robust stream to improve the reception performance of an Advanced Television Systems Committee Vestigial Sideband (VSB) Digital Television (DTV) system that is an American-type digital terrestrial broadcasting system.
2. Description of the Related Art
The ATSC VSB DTV system that is an American-type digital terrestrial broadcasting system is a single-carrier system that provides one field sync signal for each unit of 312 data segments. Accordingly, this system exhibits poor performance over an inferior channel, particularly over a Doppler fading channel.
FIG. 1 is a block diagram of an example of a digital broadcast transmitter and a digital broadcast receiver of an American-type digital terrestrial broadcasting system complying with an ATSC Enhanced VSB (EVSB) DTV system that has been proposed by Philips Electronics. The current version of this standard is ATSC Digital Television Standard A/53, Revision E, dated Dec. 27, 2005, with Amendment No. 1, dated Apr. 18, 2006, and can be downloaded from www.atsc.org. This standard is referred to hereafter as ATSC Standard A/53E. The contents of this standard are incorporated herein by reference in their entirety. This system generates and transmits a dual transport stream by adding a robust stream to a normal stream of the conventional ATSC VSB DTV system. A robust stream is a stream that has been subjected to a robust data process to provide improved reception performance compared to a normal stream over an inferior channel, particularly over a Doppler fading channel.
As shown in FIG. 1, the digital broadcast transmitter includes a randomizer 11 randomizing a dual transport stream, a Reed-Solomon (RS) encoder 12 in the form of a concatenated encoder adding parity bytes to the dual transport stream to correct errors occurring due to channel characteristics during transmission, an interleaver 13 interleaving the RS-encoded data according to a specified interleaving pattern, and a 2/3-rate trellis encoder 14 mapping the interleaved data into 8-level data symbols by performing a 2/3-rate trellis encoding of the interleaved data. The dual transport stream received by the randomizer 11 is an MPEG-2 dual transport stream, and thus the digital broadcast transmitter of FIG. 1 digital broadcast transmitter of FIG. 1 performs an error correction encoding of the MPEG-2 dual transport stream. The digital broadcast transmitter of FIG. 1 is an 8-VSB system because the trellis encoder 14 maps the interleaved data into 8-level data symbols.
The digital broadcast transmitter further includes a multiplexer (MUX) 15 multiplexing a field sync signal and a segment sync signal with the data symbols from the trellis encoder 14 to obtain an ATSC VSB DTV data frame having the configuration shown in FIG. 2, and a VSB modulator 16 inserting a pilot into the data symbols that have been multiplexed with the field sync signal and the segment sync signal by adding a specified DC value to the data symbols, performing a VSB modulation of the data symbols by pulse-shaping the data symbols to obtain a VSB-modulated signal, and up-converting the VSB-modulated signal to an RF channel band signal which is then transmitted over a channel.
Accordingly, in the digital broadcast transmitter of FIG. 1, a multiplexer (not shown) multiplexes the normal stream and the robust stream to obtain a dual transport stream that transmits the normal stream and the robust stream over one channel, and inputs the dual transport stream to the randomizer 11. The input data is randomized by the randomizer 11, the randomized data is outer-encoded by the RS encoder 12 serving as an outer encoder, and the outer-encoded data is interleaved by the interleaver 13 according to a specified interleaving pattern. The interleaved data is inner-encoded in units of 12 symbols and mapped into 8-level data symbols by the trellis encoder 14. A field sync signal and a segment sync signal are multiplexed with the data symbols from the trellis encoder 14 by the multiplexer 15. A pilot is inserted into the data symbols that have been multiplexed with the field sync signal and the segment sync signal by the VSB modulator 16, the data symbols with the inserted pilot are VSB-modulated and up-converted to the RF channel band signal by the VSB modulator 16, and the RF channel band signal is transmitted.
The digital broadcast receiver of FIG. 1 includes a tuner (not shown) down-converting the RF channel band signal received through the channel to a baseband signal, a VSB demodulator 21 performing sync detection and demodulation on the baseband signal, an equalizer 22 compensating the demodulated signal for channel distortions such as multipath, a Viterbi decoder 23 correcting errors in the equalized signal to obtain data symbols and decoding the data symbols to obtain decoded data, a deinterleaver 24 deinterleaving the decoded data according to the specified interleaving pattern used by the interleaver 13 of the digital broadcast transmitter, an RS decoder 25 correcting errors in the deinterleaved data, and a derandomizer 26 derandomizing the error-corrected data from the RS decoder 25 and outputting an MPEG-2 dual transport stream.
Accordingly, the digital broadcast receiver of FIG. 1 recovers the original signal inputted to the randomizer 11 of the digital broadcast transmitter of FIG. 1 by reversing the operations performed by the digital broadcast transmitter of FIG. 1 by down-converting the RF channel band signal to the baseband signal, demodulating and equalizing the baseband signal, and performing a channel decoding operation on the baseband signal.
FIG. 2 shows an ATSC VSB DTV data frame having the field sync signal and the segment sync signal that is used in the American-type digital terrestrial broadcasting system. As shown in FIG. 2, one frame consists of two fields, and one field consists of one field sync segment as the first segment, and 312 data segments. In the ATSC VSB DTV data frame, one data segment corresponds to one MPEG-2 packet, and consists of a 4-symbol segment sync signal and 828 data symbols.
The field sync signal and the segment sync signal shown in FIG. 2 are used for synchronization and equalization in the VSB demodulator 21 and the equalizer 22 in the digital broadcast receiver of FIG. 1. That is, the field sync signal and the segment sync signal are known data known to both the digital broadcast transmitter and the digital broadcast receiver of FIG. 1 which is used as a reference signal for the equalization performed by the equalizer 22 in the digital broadcast receiver of FIG. 1.
As discussed above, the digital terrestrial broadcasting system of FIG. 1 generates and transmits a dual transport stream by multiplexing the robust stream with the normal stream of the conventional ATSC VSB DTV system so that the robust stream is transmitted together with the conventional normal stream.
However, the digital terrestrial broadcasting system of FIG. 1 cannot improve the poor reception performance of the conventional normal stream over a multipath channel even when the dual transport stream with the multiplexed robust stream is transmitted. That is, the reception performance of the conventional normal stream is not improved at all even when the dual transport stream is transmitted. In addition, the reception performance of the robust stream over the multipath channel does not show any great improvement.